_module_comgen_words_and_files() fed untrusted text (module names read
off disk, LOADEDMODULES, MODULEPATH) straight into `compgen -W`, which
performs a full unquoted-word expansion on its wordlist -- including
command substitution -- as a normal, documented part of its behavior.
A module name, loaded-module entry, or MODULEPATH component containing
e.g. `$(...)` therefore ran arbitrary shell code the moment a user
pressed Tab.